This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We are planning to use native mass spectrometry to determine the subunit stoichiometry of a very large (>2MDa) membrane spanning protein complex - the Type 3 Secretion System. The Type 3 Secretion System is involved in injection of virulence factors by pathogen such as salmonella.